I asked my brother, who lives in Birmingham and has driven to WDW several times a year for quite a few years. He has tested every reasonable route that he can think of. The basic answer to your question is Hwy280 thru Columbus, connecting with I75 in Valdosta -- but he is the type of person who will give you way more information than you ask for (as you will see below). Here are his detailed directions, along with info on stops along the way. Have a great trip.
Fastest way from Birmingham ....
280 to/thru Columbus [crosses the Parkway near Opelika, past Tiger Town on the right, joins I-85N for a couple of exits to bypass Opelika, then off to the right to Phenix City & Columbus]
Continue to/thru Columbus GA ... 280 joins GA520 as it leaves Columbus
Continue straight on GA520 toward Dawson when US280 turns left toward Plains [at a light "in" Richland]
Continue straight on GA 520, which joins US82 in Dawson, and on thru Sasser [stop at Mark's Melon Patch on right after Sasser], and to Albany
Take Albany bypass [still with US82 for a while] around Albany to GA133 to/thru Moultrie, and on to I-75S at Valdosta.
NOTE: GA133 turns left at a traffic light in Moultrie. It also veers right just beyond either Doe Run or Morven. But it's all marked.
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The only 2-lane stretch is between Albany and Valdosta. But it's at least as quick as going from Albany over to Tifton and down I-75S.
Chic-Fil-A and more at Tiger Town.
Chic-Fil-A on right just before you get to Columbus.
Once you get on the Albany bypass, there are a few eating places at the first or second exit. You can't see them from the road, though. Watch the signs. There's a Cracker Barrel up there a few blocks away from the bypass. Good place for bathroom.
Another Chic-Fil-A near the Valdosta exit ... if you cross the interstate and go a few blocks ... on the left.
And remember that there's Target at the Archer exit in FL. [Archer -> Target] Also Sonny's ... and Chic-Fil-A, I think. You don't see the Target coming. That's our stop if we think of something we'll need at WDW.
And if you have time for ice cream .... or it's time for a sandwich ... get off at Micanopy, just below Gainesville. Go east from the interstate until you find the turn. About a mile into the town area. You'll find the ice cream & sandwich shop. Also antique shops. Just remember the way back out!
